Method for the correction of a defect in a liquid crystal display device

ABSTRACT

Laser beam irradiation spots are formed in a delta arrangement on a defective pixel present in a liquid crystal panel so that liquid crystal molecules in areas surrounding the irradiation spots are oriented vertically. Alternatively, an aligning film in a defective pixel is irradiated with a laser to form minute grooves in a different direction than the rubbing direction of the aligning film, whereby the orientation of the liquid crystal is changed so that the liquid crystal between the aligning films is no longer twisted. Thereby, a defective pixel present in a liquid crystal display panel can be made inconspicuous, and as a result, degradation of the display quality of the liquid crystal display device after correction can be prevented.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a method for the correction of adefective pixel in a liquid crystal display device, and in particular,to a method for the correction of a defect in a liquid crystal displaydevice, wherein a defective pixel is corrected by irradiation with laserbeams.

(2) Description of the Prior Art

Liquid crystal display devices can be driven at low voltages and lowelectric power, and have been utilized and commercially available assmall, thin-type flat panel displays in a wide range of products.Matrix-type liquid crystal display devices are known as one type of suchliquid crystal display devices. In particular, a liquid crystal displaydevice with an active matrix driving system is configured such thatswitching elements such as TFTs (Thin Film Transistors) or MIM (MetalInsulator Metal) Diodes, or the like, are connected to pixel electrodeswhich are arranged in a matrix-like pattern on one of a pair of glasssubstrates which are bonded together. Selection and non-selection of allthe pixel electrodes is carried out by the switching operation of theseswitching elements, to achieve display operation. For this reason, aliquid crystal display device of an active matrix driving type does notexhibit crosstalk at the time of non-selection, therefore achieving highquality display. Such crosstalk is a drawback of liquid crystal displaydevices of a simple matrix driving type.

Since the aforementioned switching element generally has a multi-layeredstructure consisting of semiconductor layer(s), insulation layer(s), andvarious types of electrodes for driving of the liquid crystal, which arelayered onto a glass substrate, patterning of the layers onto the glasssubstrate is repeated in order to manufacture the switching element. Forthis reason, there are cases in which defective switching elements whichdo not function normally due to disconnection, short-circuit, or thelike, are produced at the time of manufacture of the switching elements.Thus, pixels comprising pixel electrodes connected to defectiveswitching elements become defective pixels to which voltage can not beapplied. Particularly in the case of liquid crystal display devices inNormally White Mode, which is a display operation mode wherein thedisplay screen is white when voltage is not applied, these defectivepixels are found as bright-spot defects through which light isconstantly transmitted. Besides a defect in the switching element,damage to a pixel electrode or aligning film can also cause a brightspot.

Various methods for correcting bright-spot defects by using laser beamsto irradiate the area around the bright-spot defect in the liquidcrystal display panel have been proposed as methods for the correctionof bright-spot defects in liquid crystal display devices. For instance,in the case of "A Liquid Crystal Display Device" of Japanese PatentApplication Laid-Open Hei 1 No. 187,532, a method is disclosed whichreduces the amount of light transmitted through a defective pixel byusing laser beams to damage a polarizing plate in the area of thedefective pixel. In the case of "A Method for the Manufacture of anActive Liquid Crystal Panel" of Japanese Patent Application Laid-OpenHei 3 No. 21,928, a method is disclosed for reducing the amount of lighttransmitted through a defective pixel by means of burning the colorfilter of the defective pixel with laser beams so that it becomes gray,and heating the rubbing surface on the side of the pixel electrode sothat the orientation of liquid crystal is disturbed. Furthermore, in thecase of "A Liquid Crystal Display Device and A Method for the Correctionof A Defect in A Liquid Crystal Display Device" of Japanese PatentApplication Laid-Open Hei 4 No. 301,615, there is disclosed a method forreducing the amount of light transmitted through a defective pixel bymeans of using laser beams to form an indentation on the glass substratecorresponding to the defective pixel, and roughening its bottom surface.In the case of "A Method for the Correction of A Defect in A LiquidCrystal Display Device" of Japanese Patent Application Laid-Open Sho 60No. 243,635, there is disclosed a method for reducing the amount oflight transmitted through a defective pixel by using laser beams toirradiate the area of the defective pixel in order to burn aligning filmand pixel electrode material so that they lose their capability tocontrol the orientation of the liquid crystal layer, whereby theorientation of the liquid crystal molecules in this area becomes random.

However, in the case of each of the aforementioned methods for thecorrection of a bright-spot defect in a liquid crystal display device,the amount of light transmitted through the defective pixel is merelyreduced to an intermediate level (an intermediate tone) between thatcharacteristic of a voltage-activated state and voltage nonactivatedstate; the light transmitted through the defective pixel is notcompletely blocked.

For this reason, when a liquid crystal display device wherein adefective pixel has been corrected to an intermediate tone as above isused in a magnifying projection-type liquid crystal projectionapparatus, all of the pixels are magnified so that the defective pixelwhich has been corrected is also magnified. Thus, in such cases, theproblem occurs that the defective pixel is conspicuous and causes adecline in the quality of the projected image when the amount of lighttransmitted through the defective pixel is merely reduced to anintermediate tone.

Furthermore, none of the aforementioned methods for correction of abright-spot pixel clearly mention the amount of energy of the laser beamapplied to the defective pixel. When a laser beam is used to correct adefective pixel, it is normally necessary to irradiate substantially theentire surface of the defective pixel with the laser beam. Due to this,if the defective pixel is irradiated with laser beams at an energy levelequal to or higher than a prescribed value, the problem occurs that eventhe adjacent, normal pixels are affected, resulting in degradation ofthe display quality of the liquid crystal display device aftercorrection.

Specifically, as shown in FIG. 1, when a laser beam is used to correct abright-spot pixel, an irradiation spot 19a, whose shape corresponds tothat of a bright spot pixel 18 in a correction area 6a, and a laserirradiation-affected area 20a are generally formed. In this case, sincethe irradiation spot 19a is made large enough to correct the bright-spotpixel 18, the laser irradiation-affected area 20a also becomes large,such that pixels 17 adjacent to the bright-spot pixel 18 are affected.Thus, when the bright-spot pixel 18 is corrected, the adjacent normalpixels 17 are affected by the laser beam, resulting in deterioration ofthe display quality of the liquid crystal display device aftercorrection.

SUMMARY OF THE INVENTION

The present invention has been achieved in view of the above problemsand it is therefore an object of the present invention to provide amethod for the correction of a defect in a liquid crystal display deviceby which it is possible to prevent a decline in the display quality ofthe liquid crystal display device after correction of a defective pixel,by almost completely eliminating the transmission of light through thedefective pixel, and by eliminating the effect of laser beam irradiationon normal pixels adjacent to the defective pixel.

The present invention was attained in order to achieve theaforementioned object, and its gist resides in that a method for thecorrection of a defect in a liquid crystal display device equipped witha transmission-type liquid crystal display panel wherein liquid crystalis sealed between a pair of transparent electrodes, pixels for displayare arranged in a matrix-like pattern, and display operations areperformed by twisted-nematic mode, is characterized such that liquidcrystal molecules in the liquid crystal layer of a defective pixelpresent in the liquid crystal display panel are aligned in a verticaldirection.

Furthermore, in the above case, it is effective to irradiate theaforementioned defective pixel with laser beams in order to verticallyorient the liquid crystal molecules in the liquid crystal layer of theaforementioned defective pixel.

Furthermore, in the above case, it is effective to perform irradiationwith the aforementioned laser beam in a dispersed manner so that two ormore irradiation spots are formed on the defective pixel.

Furthermore, in the above case, it is effective to perform irradiationwith the aforementioned laser beam in such a way that the irradiationspots are arranged on the defective pixel in a triangular pattern inwhich they each constitute the apex of a triangle.

The present invention is first configured as above. As a result ofvertically orienting the liquid crystal molecules in the liquid crystallayer of the defective pixel, light is transmitted through the liquidcrystal layer without being twisted, therefore it is blocked by apolarizing plate in Normally White Mode and is transmitted through apolarizing plate in Normally Black Mode in the case of a liquid crystaldisplay panel which performs display operations in twisted-nematic mode.The amount of light transmitted through the defective pixel can thus becontrolled by vertically orienting the liquid crystal molecules.Accordingly, the defective pixel present in the liquid crystal displaypanel can be made inconspicuous, and as a result, a decline in thedisplay quality of the liquid crystal display device after correctioncan be prevented. In the above cases, the transparent electrode andaligning film of the defective pixel are burned at the irradiation spotsdue to irradiation on the defective pixel with laser beams. Thus, theliquid crystal molecules in the liquid crystal layer of the defectivepixel are oriented randomly at the irradiation spots due to the absenceof transparent electrode and aligning film, whereas they are orientedvertically in the areas around the irradiation spots due to applicationof electric field by transparent electrode. Therefore, the spotsirradiated by laser beams on the defective pixel allow light of anintermediate tone to transmit therethrough, whereas the amount oftransmitted light can be regulated in the areas surrounding the laserbeam irradiated spots. Accordingly, the defective pixel present in theliquid crystal display panel, as a whole, can be made inconspicuous, andas a result, a decline in the display quality of the liquid crystaldisplay device after correction can be prevented. Furthermore, byperforming irradiation in a dispersed manner so that two or moreirradiation spots are formed on the defective pixel, it is possible toincrease the area around the irradiation spots, that is, the areaaffected by the laser beam. This feature enlarges area in which theliquid crystal molecules corresponding to the defective pixel arevertically oriented, whereby it is possible to enlarge the area in whichthe amount of light transmitted through the defective pixel can becontrolled. Therefore, the defective pixel present in the liquid crystaldisplay panel can be made even less conspicuous and a decline in thedisplay quality of the liquid crystal display device after correctioncan be prevented. Furthermore, by performing irradiation with the laserbeam in such a way that irradiation spots are arranged on the defectivepixel in a triangular pattern in which they each constitute the apex ofa triangle, the arrangement of the laser beam irradiation spots formedon the defective pixel can be made a delta arrangement. Thus, byconfining the laser beam irradiation spots to within the defectivepixel, the area around the irradiation spots which is affected by thelaser beam can also be limited to within the defective pixel. Thus, whenthe defective pixel is irradiated with the laser beam, the effect of thelaser beam on the normal pixels adjacent to the defective pixel can bereduced, so that only the defective pixel is corrected. As a result, adecline in the display quality of the liquid crystal display deviceafter correction can be prevented.

Another gist of the present invention resides in that a method for thecorrection of a defect in a liquid crystal display device equipped witha transmission-type liquid crystal display panel wherein liquid crystalis sealed between a pair of transparent electrodes, pixels for displayare arranged in a matrix-like pattern, and display operations areperformed by twisted-nematic mode, is characterized in that an aligningfilm in a defective pixel is irradiated with laser beams via a means foradjusting groove direction which adjusts the direction of grooves formedon the surface of the aligning film, such that minute grooves with anorientation different from the rubbing direction are formed, whereby theorientation of the liquid crystal is changed.

Furthermore, in the above gist of the present invention, it is effectivethat the orientation of the minute groove formed is different from therubbing direction by a right-angle. Alternatively, it is also effectivethat the means for adjusting groove direction is a slit pattern or ablazed grating.

In the method for the correction of a defect as stated above, minutegrooves with an orientation different from the rubbing direction areformed on the aligning film in the defective pixel, such that theorientation of the liquid crystal is changed, whereby the defect iscorrected. Furthermore, minute grooves are formed on the aligning filmby irradiating the aligning film with the laser beam via a slit pattern.Due to the fact that grooves with an orientation different from that ofthe grooves formed by the original rubbing process are newly formed onthe aligning film in the defective pixel by the laser beam via the slitpattern, the liquid crystal molecules are oriented along the newlyformed grooves. Thus, if grooves which are oriented at a right angle tothe rubbing direction are formed on one of the aligning films, theorientation of the grooves on the opposing aligning films becomes thesame, so that the orientation of the liquid crystal molecules is nolonger twisted. Accordingly, the rotatory polarization of the liquidcrystal molecules is lost. Since the polarizing axis of the polarizingplate on the side of the incident light is perpendicular to thepolarizing axis of the polarizing plate on the side of the outgoinglight, the incident light is blocked by the pixel, whereby thebright-spot pixel is corrected.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing how a defective pixel in a liquid crystaldisplay panel is irradiated with laser beams in a conventional methodfor the correction of a defect in a liquid crystal display device;

FIG. 2 is a cross-sectional view showing a liquid crystal display panelwhich is corrected in an embodiment of the present invention;

FIG. 3 is a plan view showing how a defective pixel in the liquidcrystal display panel shown in FIG. 2 is irradiated with laser beams;

FIG. 4A is a schematic view illustrating the state of orientation ofliquid crystal molecules when voltage is not applied;

FIG. 4B is a schematic view illustrating the state of orientation ofliquid crystal molecules when voltage is applied;

FIG. 5 is a schematic diagram of the configuration of a defectcorrection system configured for application of a method for thecorrection of a defect in a liquid crystal display device of respectiveembodiments of the present invention;

FIG. 6 is a schematic view showing the state of a liquid crystal panelwhich has been corrected using the defect correction system of FIG. 5,as seen from the side of the active matrix substrate, in the case thatit is irradiated with light from the side of the opposing substrate whenvoltage is not applied;

FIG. 7 is an illustration showing the direction of the slit pattern ofthe mask in relation to the rubbing direction of the aligning film onone side of the liquid crystal panel in a first example of the secondembodiment of the present invention;

FIG. 8A is a schematic view showing the orientation of liquid crystalmolecules in a pixel prior to correction.

FIG. 8B is a schematic view showing the orientation of liquid crystalmolecules in a pixel after correction;

FIG. 9 is an illustration showing the orientation of a blazed grating inrelation to the rubbing direction of an aligning film in a secondexample of a method for the correction of a defect in a liquid crystaldisplay device in the second embodiment; and

FIG. 10 is an illustration showing the orientation of a slit pattern inrelation to the rubbing direction of an aligning film in a third exampleof a method for the correction of a defect in a liquid crystal displaydevice in the second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is explained as follows using theattached diagrams.

A liquid crystal display device to which a method of the presentinvention for the correction of a defect in a liquid crystal displaydevice is applied has a liquid crystal panel (liquid crystal displaypanel) 7, as shown in FIG. 2. This liquid crystal panel 7 is configuredsuch that a liquid crystal layer 11 is held between an active matrixsubstrate 12 and an opposing substrate 16, which are placed oppositeeach other.

Pixel electrodes 13, which are arranged in a matrix-like pattern and TFT10 switching elements, which are connected to the pixel electrodes 13have been formed on the glass surface of the aforementioned activematrix substrate 12. Opposing electrodes 15, which face theaforementioned pixel electrodes 13, have been formed on the glasssurface of opposing substrate 16. Thus, the aforementioned liquidcrystal panel 7 is a transmission-type liquid crystal display panel.

The aforementioned pixel electrodes 13, which consist of a transparentconductive film such as an ITO film, or the like, form pixels 17 in amatrix-like pattern on liquid crystal panel 7, as shown in FIG. 3. Thus,selection and non-selection of all the pixel electrodes 13 on theaforementioned active matrix substrate 12 is carried out by theswitching operation of the aforementioned TFT 10, and voltage isselectively applied to pixels 17, resulting in display operation.

Furthermore, the aligning films 14 and 14 are formed on theaforementioned active matrix substrate 12 and opposing substrate 16 withtheir surfaces in contact with the liquid crystal layer 11. The aligningfilms 14 and 14 twist the orientation of the liquid crystal molecules inthe liquid crystal layer 11 substantially 90°.

The typical diagrams given in FIGS. 4A and 4B illustrate the states oforientation of the liquid crystal molecules. FIG. 4A shows theorientation of the liquid crystal molecules when voltage is not applied,and FIG. 4B shows that when voltage is applied.

Specifically, polarizing plates 21 and 22 as shown in FIGS. 4A and 4Bare placed on the outer surfaces of the active matrix substrate 12 andthe opposing substrate 16 so that their polarizing axes are at a rightangle to each other. The polarizing plates 21 and 22 are placed so thatwhen light 23, which is emitted, for instance, by a back lightilluminator or the like, enters the liquid crystal layer 11 throughpolarizing plate 22 from the side of opposing substrate 16, this light23 is twisted substantially 90° in accordance with the orientation ofliquid crystal molecules 11a in the liquid crystal layer 11 whereby thelight outgoes from the polarizing plate 21 on the side of active matrixsubstrate 12.

Thus, the operation mode of the aforementioned liquid crystal panel 7 istwisted-nematic mode, and specifically, Normally White Mode, where lightis transmitted when voltage is applied and blocked when voltage is notapplied.

Specifically, in the case of the aforementioned liquid crystal panel 7which is in Normally White Mode, incident light 23 from the side of theopposing substrate 16 is transmitted through the polarizing plate 21 onthe side of the active matrix substrate 12 if no voltage is applied toliquid crystal layer 11, due to the fact that the orientation of theliquid crystal molecules 11a is twisted substantially 90°, as shown inFIG. 4A, whereas incident light 23 from the side of the opposingsubstrate 16 is blocked by the polarizing plate 21 on the side of theactive matrix substrate 12 if a voltage equal to or greater than athreshold value is applied to the liquid crystal layer 11, due to thefact that the liquid crystal molecules 11a are oriented in the directionof the electric field, that is, perpendicular to the electrodes, asshown in FIG. 4B.

Generally, TFT 10 has a multi-layered structure consisting ofsemiconductor layer(s), insulation layer(s), source/drain electrodes,gate electrodes, and the like, on a glass substrate. Thus, there arecases in which a defective TFT 10 which does not perform normalswitching operations is formed during the liquid crystal display elementmanufacturing process. Such a defective TFT 10 is unable to apply avoltage to the corresponding pixel electrode 13, resulting in theformation of a defective pixel electrode 9 (FIG. 2) which is unable toapply a voltage to the liquid crystal layer 11.

Such a defective pixel electrode 9 can be found by searching for a pixel17 (FIG. 3) which is transmitting light when the liquid crystal panel 7is driven in the aforementioned Normally White Mode and a voltage isapplied to all pixel electrodes 13, in the case that light enters fromthe side of the opposing substrate 16 of the liquid crystal panel 7.Since this pixel 17 which is in a transmissive state is always in astate of transmitting light (a bright-spot state) regardless of whetheror not a voltage is applied to the liquid crystal layer 11, thedefective pixel 17 shall be referred to as bright-spot pixel 18.

A method for correcting a bright-spot pixel 18 formed in theaforementioned liquid crystal panel 7 is explained below with referenceto the accompanied diagrams. In the present embodiment, an excimer laseris used as a laser light source and XeF is used as the laser filler gas,at an oscillation wavelength of 351 nm which is transmissible throughthe glass surface. Since an excimer laser is the processing-use laserwith the shortest oscillation wavelength, it allows high-precisionprocessing without damage to precision of formation.

First, a defect correction system utilized in the method of the presentembodiment for the correction of a defect in a liquid crystal displaydevice is explained.

As shown in FIG. 5, the aforementioned defect correction system isequipped with an excimer laser oscillator 1 as a laser light source, andhas a mask 2, a UV-reflection mirror 4, a lens 5, a liquid crystal panel7, and a liquid crystal panel mount 8, which are arranged in the aboveorder along the optical path of laser beams emitted by the excimer laseroscillator 1, starting from the side of the excimer laser oscillator 1.Specifically, a laser beam 3 emitted from the aforementioned excimerlaser oscillator 1 passes through slits in the mask 2 and is reflectedby the UV-reflection mirror 4, thereafter it passes through lens 5 andconverges on the correction area 6 on the liquid crystal panel 7 whichis mounted on the liquid crystal panel mount.

The laser beam 3 of the aforementioned excimer laser oscillator 1 is setat an output level such that it can burn a defective pixel electrode 9,the opposing electrode 15 which faces the defective pixel electrode 9,and aligning films 14 and 14 of the liquid crystal panel 7 (areas with amesh pattern in FIG. 2), when it converges on correction area 6 of theliquid crystal panel 7.

As shown in FIG. 3, the aforementioned mask 2 is formed with slits whichallow formation of multiple irradiation spots 19 by laser beam 3 onbright-spot pixel 18 in correction area 6 of the liquid crystal panel 7.In this case, the mask 2 is formed with slits which cause irradiationspots 19 to have an arrangement such that they each constitute the apexof a triangle, namely, a delta arrangement. Thus, irradiation spots 19are formed by laser beam 3 on bright-spot pixel 18 in a deltaarrangement.

The method for correction of bright-spot pixel 18 in the liquid crystalpanel 7 using the aforementioned defect correction system is explainednext. Here, the size of the opening of the aforementioned bright-spotpixel 18 is 60×60 μm, and in accordance with this, the laser beam 3emitted from the aforementioned excimer laser oscillator 1 is set up tohave a pulse number of 10, an energy density of 0.7 J/cm, a frequency of1 Hz, and a beam diameter of 60 μm, whereas the diameter of the slits ofmask 2 is set at 10 μμm.

First, the bright-spot pixel 18 in the liquid crystal panel 7 should bechecked. With the polarizing plates attached above and below the liquidcrystal panel 7, voltage is applied, the state of transmission of lightis observed, and a pixel which is transmitting light is recognized as abright-spot pixel 18, provided that the operation mode of the liquidcrystal panel 7 is Normally White Mode.

Next, after the location of bright-spot pixel 18 has been confirmed, theliquid crystal panel 7 is mounted on the liquid crystal panel mount 8 atthe prescribed position, and the correction area 6 is set up accordingto the position of the bright-spot pixel 18. At this time, thepolarizing plates of the liquid crystal panel 7 are removed.

After this, the laser beam 3, which is set at the prescribed outputlevel, is emitted from the excimer laser oscillator 1, and made toconverge on the correction area 6 of the liquid crystal panel 7 via mask2, UV-reflection mirror 4, and lens 5, in order to correct thebright-spot pixel 18. After correction of the bright-spot pixel 18, thepolarizing plates are again fitted onto the liquid crystal panel 7.

Thus, as shown in FIG. 3, irradiation spots 19 with a delta arrangementare formed on the bright-spot pixel 18 in the aforementioned correctionarea 6, and the laser irradiation-affected areas 20 which are affectedby laser beam 3 are formed concentrically around respective irradiationspots 19. At this time, since the output of laser beam 3 is set so thatit can burn pixel electrode 13, opposing electrode 15 and aligning film14, as mentioned above, the defective pixel electrode 9, the opposingelectrode 15 corresponding to this defective pixel electrode 9, and thealigning films 14 and 14, as shown in FIG. 2, are burned by theirradiation spots 19 on the bright-spot pixel 18, whereas, in the laserirradiation-affected areas 20, the defective pixel electrode 9 and theopposing electrode 15 remain.

Accordingly, the liquid crystal molecules are oriented randomly in theliquid crystal layer 11 corresponding to irradiation spots 19, sincedefective pixel electrode 9, opposing electrode 15 and aligning films 14and 14 are gone from this area, whereas in the liquid crystal layer 11corresponding to the laser irradiation-affected areas 20, since only thealigning films 14 and 14 are gone while the defective pixel electrode 9and the opposing electrode 15 are remaining, the liquid crystalmolecules have an electric field applied thereto by the remainingelectrodes and are thus oriented in the direction of the electric field,that is, perpendicular to the substrates.

That is, when polarizing plates are placed on its upper and lower sidesof the liquid crystal panel 7 after correction of the bright-spot pixel18 and voltage is applied, the liquid crystal panel 7 does hardly allowlight transmitted from the side of opposing substrate 16, to passthrough the corrected bright-spot pixel 18, as shown in FIG. 6. Theareas of the liquid crystal panel 7 through which light is transmittedare shown here as void areas, whereas the areas where light is blockedare shown as areas with slanted lines.

Specifically, the liquid crystal molecules at irradiation spots 19 onthe bright-spot pixel 18 which has been irradiated with laser beam 3,are oriented randomly so that the amount of light transmitted isintermediate between the amount usually transmitted when voltage isapplied and when voltage is deactivated, that is, the luminance is at anintermediate level. At the laser irradiation-affected areas 20 on thebright-spot pixel 18, the liquid crystal molecules are orientedvertically so that the light is blocked by the polarizing plates.

Thus, it is possible to make a bright-spot area on the liquid crystalpanel 7 inconspicuous by irradiating the bright-spot pixel 18 with laserbeam 3 in the above manner, thus markedly reducing the amount of lighttransmitted through bright-spot pixel 18. Thereby a decline in imagedisplay quality can be prevented when a liquid crystal panel 7 withcorrected bright-spot pixels 18 is used in a liquid crystal displaydevice. For instance, in the case that a liquid crystal panel 7 withbright-spot pixels 18 which have been corrected is used in a magnifyingprojection-type liquid crystal projection device, degradation of theprojected image quality can be prevented since the defective pixelswhich have been corrected are inconspicuous even when the pixels aremagnified.

Furthermore, in the present invention, the area affected by laser beam 3can be reduced in size because irradiation spots 19 are formed on thebright-spot pixel 18 in a delta arrangement, as shown in FIG. 3, incontrast with aforementioned FIG. 1. Thus, even when a bright-spot pixel18 is corrected by irradiation with laser beam 3, it can be corrected byitself without affecting the normal pixels 17 adjacent to thisbright-spot pixel 18. As a result, the display quality of the liquidcrystal display device after correction can be improved.

Though the output of laser beam 3 is set at the aforementionedconditions for the purposes of the present embodiment, it is not limitedto these. For instance, the energy density of laser beam 3 may be madevariable. In this case, if the energy density of laser beam 3 is set ata value lower than in the above embodiment, the laserirradiation-affected areas 20 which are formed will become smaller,whereas if the energy density of laser beam 3 is set at a value higherthan in the above embodiment, the laser irradiation-affected areas 20which are formed will become larger. By thus making the energy densityof laser beam 3 change, it is possible to change the size of the areawhere vertically oriented liquid crystal molecules are present in thebright-spot pixel 18. Thus, it is possible to change the amount of lighttransmitted through the bright-spot pixel 18 at will.

The method of the above embodiment for the correction of a defect in aliquid crystal display device, is applied to a transmission-type liquidcrystal display device with a liquid crystal display panel whereinliquid crystal is sealed between a pair of transparent electrodes,pixels for display are arranged in a matrix-like pattern, and displayoperations are performed by twisted-nematic mode. In such a device, themethod of the embodiment corrects a defective pixel by verticallyorienting liquid crystal molecules in the liquid crystal layer of thedefective pixel.

Therefore, the defective pixel present in the liquid crystal displaypanel can be made inconspicuous, and as a result, a decline in thedisplay quality of the liquid crystal display device after correction ofthe defect can be prevented.

In addition to the above effect, if the defective pixel is corrected byirradiating it with laser beams in order to vertically orient the liquidcrystal molecules in the liquid crystal layer, the liquid crystalmolecules in the liquid crystal layer of the defective pixel can be madeto be oriented randomly in the irradiation spots and to be orientedvertically in the areas surrounding the irradiation spots.

Thus, the spots irradiated by the laser beams on the defective pixelallows light of intermediate tone to transmit therethrough, whereas thetransmission of light through the areas surrounding the laser-beamirradiated spots can be suppressed. Accordingly, the defective pixelpresent in the liquid crystal display panel can be made inconspicuouswhereby a decline in the display quality of the liquid crystal displaydevice after correction can be prevented.

Furthermore, in addition to the above, if the defective pixel iscorrected by performing irradiation with laser beams in such a dispersedmanner that two or more irradiation spots are formed on a singledefective pixel, the area where the liquid crystal molecules arevertically oriented is enlarged, whereby it is possible to establish anenlarged area that blocks transmission of light in the defective pixel.

Thus, since the area on the defective pixel where the amount of lighttransmitted can be suppressed is enlarged, the defective pixel presentin the liquid crystal display panel can be made inconspicuous whereby adecline in the display quality of the liquid crystal display deviceafter correction can be prevented.

Furthermore, when the defective pixel is corrected by irradiation withlaser beams in such a way that the irradiation spots are arranged on thedefective pixel in a triangular pattern in which they each constitutethe apex of a triangle, the defective pixel alone is corrected becauseit is possible to reduce the influence of the irradiation spots by thelaser beam on adjacent pixels.

Another embodiment of the present invention is explained next usingdiagrams.

The defect correction system used is the system of FIG. 5 described inthe explanation of the previous embodiment. In this system, abright-spot pixel is corrected by forming grooves on the aligning filmin the area of the defective pixel so that the direction of the groovesis different from that of the grooves formed during the original rubbingprocess. Mask 2 in the aforementioned system of FIG. 5 is used for thispurpose as a means for adjusting the groove direction. In a firstexample, the slit pattern used for the slits of the mask 2 is used.

FIG. 7 is an illustration of the first example, showing the direction ofthe slit pattern of the mask 2 in relation to the rubbing direction ofthe aligning film 14 on one side of the liquid crystal panel 7. In FIG.7, the groove direction 29 of the slit pattern of the mask 2 and therubbing direction 30 of the aligning film 14 are placed at right angles.Due to the action of the slits placed in this manner, the irradiationspots made by laser beam 3 are partitioned in a direction perpendicularto the rubbing direction of the aligning film, whereby new grooves witha width of a few hundred nm are formed in a direction perpendicular tothe direction of the grooves formed on the aligning film 14 by theoriginal rubbing process. Thus, the direction of the grooves on theopposing aligning films 14 becomes the same.

FIGS. 8A and 8B are schematic diagrams respectively showing theorientation of liquid crystal molecules in a pixel prior to and afterestablishment of new grooves in the aligning film 14. As can be seenfrom these diagrams, by making the groove direction of the opposingaligning films 14 the same, the state shown in FIG. 8A in which theorientation of the liquid crystal molecules 11a is twisted 90° can bechanged to the state shown in FIG. 8B in which the liquid crystalmolecules 11a are no longer twisted. Specifically, the bright-spot pixelcan be corrected due to the fact that the rotatory polarization of theliquid crystal molecules 11a is lost and the polarizing axis 25 of thepolarizing plate 22 on the side of the incident light is at a rightangle with the polarizing axis 26 of polarizing plate 21 on the side ofthe outgoing light, whereby the transmitted light 23 is blocked.

In this case, the laser 3 can be used to make grooves in either theupper or lower aligning film 14.

Next, FIG. 9 shows a second example of the method of the secondembodiment for the correction of a defect in a liquid crystal displaydevice, in which case a blazed grating 27 is used as a means foradjusting the groove direction. That is, it shows the orientation of theblazed grating 27 in relation to the rubbing direction 30 of thealigning film 14. In the figure, a reference numeral 28 indicates thegroove direction of blazed grating 27 whereas a reference numeral 3indicates a laser beam. In the same manner as in the case of the slitpattern of FIG. 7, except for the fact that blazed grating 27 is usedinstead of the slit pattern of the mask 2 in FIG. 7, the irradiationspots made by the laser beam 3 are partitioned by the blazed grating 27so that minute grooves can be formed on the aligning film 14.

Furthermore, FIG. 10 shows a third example of the method of the secondembodiment for the correction of a defect in a liquid crystal displaydevice. In this example, the groove direction 30 of the slits in thefirst example above is oriented at will at any angle other than a rightangle in relation to the rubbing direction 29 of the aligning film. Byirradiation with laser beam 3 via the mask 2, which is placed at anangle other than a right angle, new grooves are formed on the aligningfilm 14 at an angle other than a right angle in relation to the groovesformed by the original rubbing process. By forming grooves at an angleother than a right angle, the angle of twisting of orientation of theliquid crystal molecules 11a is adjusted to give the corrected pixel anintermediate tone between that of a bright-spot and a black spot.

In the above example, the closer the angle of the slit groovesapproaches a right angle in relation to the groove direction of thealigning film 14, the closer the tone of the corrected pixel can be madeto that of a dark spot, whereas the closer it approaches being parallelto it, the closer it can be made to that of a bright-spot. That is, bymodifying the direction of the grooves, the pixel can be adjusted to beany intermediate tone at will.

Furthermore, in the modes shown in FIG. 7 or FIG. 10 above, the laserenergy amount can be modified by adjusting the width of slits 2.

As evident from the above embodiment, since the aligning film isirradiated with laser beams via a means for adjusting groove directionsuch as a slit pattern, blazed grating, or the like, the energy level ofthe laser beam at the irradiated surface is low. As a result, thepresent invention makes it possible to correct a defective pixel byitself without affecting other pixels.

What is claimed is:
 1. A method for the correction of a defect in aliquid crystal display device equipped with a transmission-type liquidcrystal display panel wherein liquid crystal is sealed between a pair oftransparent electrodes, pixels for display are arranged in a matrix-likepattern, and display operations are performed by twisted-nematic mode,said method comprising the steps of:determining a location of adefective pixel; removing polarizing plates from said liquid crystaldisplay panel; irradiating said defective pixel by local laserirradiation at a setting sufficient to bum pixel electrode, opposingelectrode and aligning film, forming irradiation spots having defectivepixel electrode, opposing electrode and aligning films removedtherefrom, said irradiation spots having liquid crystal moleculesoriented randomly so that an amount of light transmitted is intermediateto an amount transmitted when voltage is applied and an amounttransmitted when said voltage is deactivated: formingirradiation-affected areas having only aligning films removed therefromand having liquid crystal molecules oriented vertically so that lighttherefrom is blocked by said polarizing plates; and replacing saidpolarizing plates on said liquid crystal display panel.
 2. A method forthe correction of a defect in a liquid crystal display device accordingto claim 1, wherein said defective pixel is irradiated with laser beamsin order to vertically orient the liquid crystal molecules in the liquidcrystal layer of said defective pixel.
 3. A method for the correction ofa defect in a liquid crystal display device according to claim 2,wherein irradiation is performed with said laser beam in a dispersedmanner so that two or more irradiation spots are formed on the defectivepixel.
 4. A method for the correction of a defect in a liquid crystaldisplay device according to claim 3, wherein irradiation is performedwith said laser beam in such a way that the irradiation spots arearranged on the defective pixel in a triangular pattern in which theyeach constitute the apex of a triangle.
 5. A method for the correctionof a defect in a liquid crystal display device equipped with atransmission-type liquid crystal display panel wherein liquid crystal issealed between a pair of transparent electrodes, pixels for display arearranged in a matrix-like pattern, and display operations are performedby twisted-nematic mode, said method comprising the steps of:determininga location of a defective pixel, determining a direction of groovesformed in an aligning film during an original rubbing process;irradiating with a laser beam proximate to said defective pixel andforming laser grooves in said aligning film, said laser grooves havingan orientation different from the direction of grooves formed in saidaligning film during said original rubbing process.
 6. A method for thecorrection of a defect in a liquid crystal display device according toclaim 5, wherein the orientation of said minute groove formed isdifferent from the rubbing direction by a right-angle.
 7. A method forthe correction of a defect in a liquid crystal display device accordingto claim 5 or 6, wherein the means for adjusting groove direction is aslit pattern.
 8. A method for the correction of a defect in a liquidcrystal display device according to claim 5 or 6, wherein the means foradjusting groove direction is a blazed grating.